Can You Mix Old Gas With New Gas: Answer From An Auto Writer

If you have stored gas in your gas container or your vehicle for a long while, you might need to add new gas to the old gas when you want to use it. The possibility of mixing old and new gas together can be daunting if you consider that old gas might be bad.

Can You Mix Old Gas With New Gas? Yes, you can mix old gas with new gas, using the new gas to dilute the old in a 4-to-1 ratio (new-to-old). You can also put in a gas additive to improve the quality of the old gas.

AutoBlog put together an article that explains that old gas might affect the performance of your engine due to oxidation and contamination. Adding a fuel system stabilizer to fresh gas can prevent it from getting oxidized fast.

Why Does Old Gas Go Bad?

Old gas goes bad due to the fact that it has been exposed to oxygen and other environmental factors that cause chemical reactions to take place in the gas, which can lead to engine problems.

You may be wondering if gas really does go bad. The average person does not examine the gas during its different stages of life. The average person would fill their gas can, put it in their lawn mower, car, or other equipment, and go about their day using it.

The term “bad gas”  simply means that the gas is old and has lost a substantial portion of its combustibility. As gas ages, its chemical characteristics alter.

Around 30 days into its life, gasoline begins to degrade. This means that if you leave gas sitting in your lawn mower or car for several weeks, it would have lost some of its quality.

Gas is a highly volatile substance, which means it vaporizes readily and may be used effectively in your car’s engine. It also means that if left unused for a while, most of its highly volatile components would evaporate over time.

Effectively, only the less volatile components of gas will be left to carry out the function of running the engine. Also, if the gas is not volatile enough, your engine will develop operational issues.

Another reason why gas would go bad is oxidation. The hydrocarbons in the gas can combine with oxygen in the air to form new compounds, modifying the chemical properties of the gas.

Therefore, if you are going to store extra gasoline for a while, make sure to do it in a cold, low-humidity, low-oxygen environment, and in an airtight container. 

How Can You Tell If Gas Has Gone Bad?

The simplest way to tell if your gas has gone bad would be to simply inspect and compare the old gas with fresh gas. Bad gas would appear darker and might smell bad or strong.

Your car comes to a complete stop in the middle of the road, and the “check engine” indicator lights up. This could be because there is a gas or oil problem that is affecting the engine.

Maybe, you decide to check the gas to see if it has gone bad. The question now is, how can you actually tell if your gas is bad?

When gas gets old, its chemical properties alter. When you subject your car or lawn mower engine to stale gas, it is not likely to run smoothly. There are several ways to tell if your gas has gone bad;

  • A way to tell if your gas has gone bad would be to check if the gas is burning properly. If it is not, the “check engine” light in your car would come on, indicating that there is an issue with your gas.
  • Another way to tell if your gas has gone bad is to simply look at it and compare it to fresh gas. Old gas would have a darker or muddier appearance combined with a bad or pungent odor.
  • If the car develops problems that prevent it from working properly, this could mean that it fails to start, has a stalled ignition, or loses power while driving, most likely at the point of acceleration.
  • To test your gas, mix a small amount with water and keep an eye out for separation. Water and gas do not and should not mix. Water, being heavier than gas, will form a separate layer beneath the gas.

Small amounts of water will appear as bubble-like spheres rolling around beneath the top layer of gas. Water causes the engine to run inefficiently and damages the fuel tank, as well as several other engine components.

So, before using any gas that is more than two months old, shake the can and pour some of it into a clear container to inspect it. Check for water or debris inside the tank or the gas container. Take a whiff; if it does not look or smell like regular gas, it might be unsafe for use.

Can I Make Old Gas Good To Use?

Yes, you can make old gas good to use by diluting it with fresh gasoline. Mix old gas with new gas in a one-to-four ratio (1 part old gas to 4 parts fresh gas), then add a gasoline additive such as an octane booster or gas stabilizer.

People expect the best from every product they buy, including vehicles, as we always require them to function properly. Every car has the potential to run at its best; that would mean enhancing the gas and/or delaying the breakdown.

When gas gets old, it loses most of its volatile components and it can affect the performance of your car. Making old gas good enough for use would mean you have to recondition the gas before it loses all its volatility.

Mixing old gas with fresh gas and petroleum additives will improve the quality of the gas and keep your petroleum-driven equipment at peak performance.

An octane booster is a type of liquid additive that is added to your car’s gas tank to increase its gas octane rating, giving you “top-grade” gas.

A gas stabilizer is a type of additive that contains chemicals such as antioxidants. Its main function is to prevent your gas from breaking down, ensuring that it maintains its quality over time.

Generally, the best way to make old gas good to use would be to dilute the old gas by filling your tank with fresh gas and then including an additive. Repeat this about two to three times, adding gas every time the gas gauge falls below half a tank.

This would dilute the old gas by mixing it with fresh gas, enabling the engine to run properly until the old gas is gone. In essence, octane boosters aid in making sure that you are “feeding” your engine with the highest quality fuel possible.

Gas stabilizers, in a way, delay the aging process of gasoline. It is also helpful to use an additive with fresh gasoline that you may want to store for a long time.

What Are Some Of The Best Additives For Old Gas?

Gas treatments, fuel injector cleaners, fuel system cleansers, fuel stabilizers, and octane boosters are some of the best additives that you can use for old gas.

Gasoline additives are compounds that are added to gasoline to increase its quality and efficiency. They either increase the octane rating of gasoline or act as protective coatings or lubricants. Gas additives can help to minimize the chance of car problems like rough running, delayed acceleration, and stalling.

Gas additives come in several forms, such as liquids, powders, and capsules. Various sorts of gas additives perform a number of functions for gas and work in a range of applications, including:

  • reducing sludge
  • managing soot
  • enhancing combustion
  • serving as a biocide to fight off impure substances

Each product is made to solve a certain issue. This might seem like a lot of information to process, but do not fret. Just make sure you find out how much and what kind of cleaning agent is used in each brand of gas additive.

Octane Booster

Octane boosters improve engine performance by increasing the octane level of the fuel while also cleaning the fuel intake system.

Gas System Cleaner

These cleaning solutions are designed to remove dirt, clogs, and other deposits while restoring the entire fuel system to its original state.

Gas Treatments

These are designed to enhance the quality of the gas you use by removing harmful materials such as soot and water that can saturate the gas.

Gas Injector Cleaner

These gasoline additives are used to clear clogs and other residues from an engine’s fuel injector, thereby recovering performance to desirable levels.

Gas Stabilizers

Gas stabilizers preserve your engine against stale gas without you having to drain it, making it easier to restart the engine when it is ready.

What Damage Will Old Gas Do To A Car?

Quite a number of issues with cars can be brought on by using or having old gas in your car. These include eroded gas tanks and carburetors, engine failures, irregular ignition, and blockages.

When gas becomes old, it has most likely lost its efficacy, which might result in damage to some of your car’s parts, such as the walls of gas tanks, spark plugs, engines, and so on. You might be wondering what type of harm outdated gas may cause to your vehicle.

Here are a few negative effects that old gas can have on a car;

Erosion and Contamination

When you leave gas in your tank for a long period, changes in temperature can produce condensation, which can corrode your gas lines and tank internally, potentially causing engine failure. Rust scales in the gas ruin the filter and gas pump, forcing you to replace them.

During the winter, pollution from condensed water in the gas might cause your gas lines to freeze and cause your engine to stop. Bacteria may also breed in condensed water, which is used to preserve old gas.


Unused gas in your car will almost certainly evaporate. That means air has entered the picture, and oxidation has occurred. Air plus time, along with the metals in your gas system, can cause oxidation.

This can cause gum and carbon deposits to build up in your gas lines, coating your carburetor or jamming your fuel injectors, obstructing gas lines, clogging your filter, and lowering the performance of your engine.

To keep gasoline from becoming a problem when unused, make sure your gas tank and lines are clean and intact. There will be no problems if there is no dust or debris present to alter the chemistry of the gas.

What Can I Do To Get Old Gas Out Of My Car?

You could either use a siphon pump with a gas container at the other end or use gas additives, such as octane boosters, to get the old gas out of your car tank.

As it ages, old gas would cause a variety of issues for your car, such as rusted gas lines, damaged filters, and other engine faults. You probably do not want to have to pay for repairs for such damages if you can prevent them. The alternative is to take out the old gas from your car.

Make certain that;

  • you own a siphon pump.
  • you have a disposable gas can (that has been certified by the authorities) either plastic or metal
  • for cleanup, you have rags, towels, or paper towels.

Before you begin, move your car to a well-ventilated place with a flat surface, such as a garage floor or driveway, and ensure that it has completely cooled down (some cars require you to run the engine to move them).

Here are the steps to follow;

  • Take off the gas tank cap, then set your government-approved disposable gas container on the flat area.
  • Put the output tube of the siphon pump into the container and the input tube into the gas tank.
  • Pump the siphon by pressing the rubber section at the top (see your siphon manual for instructions if yours is designed differently) until all of the gas has been removed.
  • Remove the siphon and pump it a few more times onto a cloth or paper towel to get any residual gas out.
  • Close the tank and containers’ lids.

Another option for getting old gas out of your car would be to use additives such as octane boosters and add gas every time the gauge drops below half a tank. This procedure will dilute the old gas with the new, allowing the engine to function normally until the bad gas has been removed.

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